Cleaning the filter in my goldfish tank is deadly! I badly lascerated my hand numerous times cleaning that sucker - even skinned my entire thumb scrubbing the intake. Blech - nothing like watching you skin float away in a bucket of dirty fish water because you're trying to keep the beneficial bacteria alive.
I seldom walk away from tank cleaning without a few cuts and bruises. Recently, while scrubbing the glass on the hood of my 75g, I ran my palm along the edge thinking the paper towel was covering it... it wasn't. Slit my whole darned palm open, blood EVERYWHERE; they should really sand that glass so the edges aren't so deadly!
I've gotten more than a few wounds from the betta tanks even since they're 100% cleanings. The 5g hex tank has a vendetta against me I swear; it is amazingly hard to grip properly because the extra sides throw it off balance no matter how you hold it. I slipped once on spilled water carrying it to the tub to dump it, and litterally just crashed onto my back and let it fall on me so it wouldn't shatter - many, many bruises from that one!